Roller bearing

ABSTRACT

The roller bearing  10  comprises a plurality of substantially cylindrical-shaped rollers  15  which are respectively interposed between a concave-shaped race surface  12  formed on an outer race  11  and a concave-shaped race surfaces  14  formed on an inner race  13 . Each of the rollers  15  is structured such that the central portion of the rolling surface thereof is formed by a first convex-shaped bus  17  which corresponds to the concave-shaped race surfaces  12  and  14 , while the two end portions of the rolling surface thereof are respectively formed by second buses  16  which have a radius of curvature smaller than the radius of curvature of the first bus  17.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a roller bearing and, inparticular, to a roller bearing including a plurality of rolling memberseach of which is formed in a substantially conical shape, asubstantially cylindrical shape, or a similar shape.

[0002] In a roller bearing including a plurality of substantiallycylindrical-shaped or substantially conical-shaped rolling members(which are hereinafter referred to as rollers), if there occurs an axisshift, that is, if the axes of outer and inner races intersect eachother, then, in a contact portion between the race surface (so called asan outer racetrack) of the outer race and the rollers and/or a contactportion between the race surface (so called as an inner racetrack) ofthe inner race and the rollers, on one side of the position there theroller end portions are contacted with the race surfaces of the innerand/or outer races, there may occur locally an increase in the contactpressure (which is hereinafter referred to as edge stress), which raisesa fear that the roller bearing may be damaged in the early stage.

[0003] Therefore, when mounting the roller bearing onto various devices,it is necessary to make the axes of the outer and inner races coincidewith each other with high accuracy, but, in fact, there is a possibilitythat the axes of the outer and inner races can be shifted/deviated fromeach other if the rotary shaft of the roller bearing is flexed due to alarge axial load.

[0004] In order to avoid the above problem, conventionally, there isused a roller bearing in which a crowning operation such as a fullcrowning operation or a partial crowning operation is performed on thesurfaces of the inner and outer races and/or the peripheral surfaces(which are hereinafter referred to as rolling surfaces) of therespective rollers (that is, a conventional roller bearing).

[0005] Here, the crowning operation means an operation which works thewhole or given areas of buses forming the surfaces of the inner andouter races or the whole or given areas of buses forming the rollingsurfaces of the rollers into convex-shaped curved surfaces.

[0006] By the way, in the above-mentioned conventional roller bearing,in a large axis shift angle (in which the axes of the outer and innerraces can be shifted/deviated from each other by a relatively largeangle), in order to prevent the edge stress from occurring between therace surfaces and the rolling surfaces, the radius of curvature of theportion to be crowned must be set small.

[0007] However, if the radius of curvature of the portion to be crownedis set small, when the axis shift angle is small (in which the axes ofthe outer and inner races can be shifted/deviated from each other by arelatively small angle), or when no axis shift occurs, the surfacepressures in the central portions of the contact portions between therespective race surfaces and rollers are inconveniently high whencompared with a case in which no crowning operation is performed or acase in which the radius of curvature of the portion to be crowned isset large.

SUMMARY OF THE INVENTION

[0008] The present invention aims at eliminating the above drawbacksfound in the conventional roller bearing. Accordingly, it is an objectof the invention to provide a roller bearing which can preventoccurrence of an edge stress in a large axis shift angle producedbetween the outer and inner races, and also, even when the axis shiftangle between the outer and inner races is small, can control anincrease in the surface pressures in the central portions of the contactportions between the surfaces of the outer and inner races and therolling surfaces of the rollers.

[0009] The above-mentioned object can be achieved by a roller bearingaccording to the present invention comprising an outer race including anouter race surface which is formed on the inner peripheral surfacethereof which is defined by rotating an outer race surface defining busabout an axis thereof, an inner race including an inner race surfacewhich is formed on the outer peripheral surface thereof and is definedby rotating an inner race surface defining bus about the axis, and aplurality of rolling members respectively interposed between the outerand inner race surfaces in which an outer peripheral surface of each ofthe rolling members is defined by rotating a rolling surface definingbus. At least one of the outer race surface defining bus, the inner racesurface defining bus and the rolling surface defining bus comprises afirst radius of curvature. Each of the others of the outer race surfacedefining bus, the inner race surface defining bus and the rollingsurface defining bus comprises,

[0010] a first bus having a second radius of curvature which isdifferent from the first radius of curvature and substantially disposedat a center in an axial direction of the roller bearing and

[0011] second buses disposed both sides of the first bus, each of thesecond buses having a third radius of curvature which is different fromthe first radius of curvature and is also different from the secondradius of curvature.

[0012] In the above-mentioned construction according to the presentinvention, it is preferable that each of the outer race surface definingbus and the inner race surface defining bus has the first radius ofcurvature, and the rolling surface defining bus comprises the first busand the second buses.

[0013] Further, in the above-mentioned construction according to thepresent invention, it is also preferable that each of the outer racesurface defining bus and the inner race surface defining bus comprisesthe first bus and the second buses, and the rolling surface defining bushas the first radius of curvature.

[0014] Moreover, in the above-mentioned roller bearing, it is preferablethat each of the outer race surface and the inner race surface is aconcave shape, and also the first radius is larger than the secondradius, and the second radius is larger than the third radius.

[0015] In addition, in the above-mentioned roller bearing, it isadvantageous that each of the outer race surface and the inner racesurface is a convex shape, and also the first radius is smaller than thesecond radius, and the second radius is smaller than the third radius.

[0016] Further in attaining the above object, according to one aspect ofthe invention, there is provided a roller bearing comprising an outerrace including a concave-shaped race surface formed on the innerperipheral surface thereof, an inner race including a concave-shapedrace surface formed on the outer peripheral surface thereof, and aplurality of substantially cylindrical-shaped rolling membersrespectively interposed between the concave-shaped race surfaces of theouter and inner races, the outer peripheral surface of each of therolling members being formed by a convex-shaped bus, wherein each ofcentral portions in one of the concave-shaped race surfaces of the outerand inner races and the outer peripheral surfaces of the rolling membersis formed by a first bus having a given radius of curvature, and two endportions respectively adjoining the central portion are respectivelyformed by second buses each having a radius of curvature which causesthe two end portions to be separate from the other of the concave-shapedrace surfaces of the outer and inner races and the outer peripheralsurfaces of the rolling members.

[0017] Also, according to another aspect of the invention, there isprovided a roller bearing comprising an outer race including aconvex-shaped race surface formed on the inner peripheral surfacethereof, an inner race including a convex-shaped race surface formed onthe outer peripheral surface thereof, and a plurality of substantiallycylindrical-shaped rolling members respectively interposed between theconvex-shaped race surfaces of the outer and inner races, the outerperipheral surface of each of the rolling members being formed by aconcave-shaped bus, wherein each of central portions in one of theconvex-shaped race surfaces of the outer and inner races and the outerperipheral surfaces of the rolling members is formed by a first bushaving a given radius of curvature, and two end portions respectivelyadjoining the central portion are respectively formed by second buseseach having a radius of curvature which causes the two end portions tobe separate from the other of the convex-shaped race surfaces of theouter and inner races and the outer peripheral surfaces of the rollingmembers.

[0018] Here, in the roller bearing according to the invention, theconcave-shaped race surfaces of the outer and inner races as well as theouter peripheral surfaces of the rolling members (or rollers) may beformed by the first and second buses which continue with each other andhave different radii of curvature.

[0019] In more particular, to form the rolling surface of each rollerusing the first and second buses, the central portion of the rollingsurface of the roller may be formed by the first convex-shaped bus whichcorresponds to the buses of the respective concave-shaped race surfacesand, at the same time, the two end portions of the rolling surface ofthe roller may be respectively formed by the second convex-shaped buseseach having a radius of curvature smaller than that of the first bus.

[0020] On the other hand, to form each of the respective concave-shapedrace surfaces of the outer and inner races, the central portion of eachof the respective concave-shaped race surfaces may be formed by thefirst concave-shaped bus which corresponds to the bus of the rollingsurface of the roller and, at the same time, the two end surface sidesof each concave-shaped race surface may be respectively formed by thesecond concave-shaped buses each having a larger radius of curvaturethan the first bus.

[0021] In addition, in the above-mentioned roller bearing according tothe present invention, it is advantageous that a center of curvature ofthe concave-shaped bus defined by the concave-shaped race surface of theouter race is positioned at a position further than the axis of theroller bearing. In this case, the edge load can be remarkably andeffectively suppressed.

[0022] Further, in the above-mentioned roller bearing according to thepresent invention, it is advantageous that a center of curvature of theconvex-shaped bus defined by the convex-shaped race surface of the innerrace is positioned at a position further than the axis of the rollerbearing. In this case, the edge load can be remarkably and effectivelysuppressed.

[0023] Also, in the above-mentioned roller bearing according to thepresent invention, the convex-shaped race surfaces of the outer andinner races as well as the outer peripheral surfaces of the rollingmembers (or rollers) may be formed by the first and second buses whichcontinue with each other and have different radii of curvature.

[0024] In more particular, to form the rolling surface of each rollerusing the first and second buses, the central portion of the rollingsurface of the roller may be formed by the first concave-shaped buswhich corresponds to the buses of the respective convex-shaped racesurfaces and, at the same time, the two end portions of the rollingsurface of the roller may be respectively formed by the secondconcave-shaped buses each having a radius of curvature larger than thatof the first bus.

[0025] On the other hand, to form each of the respective convex-shapedrace surfaces of the outer and inner races, the central portion of eachof the respective concave-shaped race surfaces may be formed by thefirst convex-shaped bus which corresponds to the bus of the rollingsurface of the roller and, at the same time, the two end surface sidesof each convex-shaped race surface may be respectively formed by thesecond convex-shaped buses each having a larger radius of curvature thanthe first bus.

[0026] In addition, in these cases, in order that the boundary linebetween the first and second buses cannot provide a ridge or a groove,the first and second buses may be so formed as to continue with eachother smoothly, or a chamfering operation may be performed along theboundary line between the first and second buses.

[0027] By the way, the above-mentioned concave-shaped race surfaces,convex-shaped race surfaces, and rolling members are not limited tothose which are formed by the first and second buses; but, they can alsobe formed by two or more kinds of buses.

[0028] In the conventional roller bearing, contact between the crownedrace surfaces and the rolling surfaces of the rollers is carried out inthe form of mutual contact between the convex-shaped buses by which therace surfaces and roller rolling surfaces are formed. On the other hand,in the above-mentioned structures according to the invention, the racesurfaces formed by convex-shaped buses are to be contacted with theroller rolling surfaces formed by buses each having a correspondingshape, that is, the roller rolling surfaces formed by the concave-shapedbuses. Thanks to this, even when the axis shift angle between the outerand inner races is small, or even when no axis shift is present betweenthe outer and inner races, there is no fear that the contact surfacepressure between the respective race surfaces and the rolling surfacesof the rollers can be increased up to a high pressure.

[0029] Also, in the present two roller bearings, since there areproduced relatively large clearances respectively between the racesurfaces and the rolling surfaces of the rollers, even if there occurs arelatively large axis shift between the outer and inner races, there isno possibility that an edge load or the like can be generated.

[0030] In addition, in the case where a bus configuration of each of theaforementioned rolling surface and race surfaces are formed by aplurality of buses having different radii of curvatures, it is possibleto connect them more smoothly at its boundary portions, to therebysuppress an increase in the surface pressures between the respectiverace surfaces and the respective rolling members.

[0031] Therefore, in these roller bearings, when compared with theconventional roller bearing, a large axis shift angle to be producedbetween the outer and inner races can be coped with properly and also,even when the axis shift angle between the outer and inner races issmall, an increase in the surface pressures between the respective racesurfaces and the respective rolling members can be controlled, wherebythe above-mentioned object of the invention can be achieved.

[0032] By the way, in these roller bearings, to control the rise in thesurface pressure in the boundary between the first and second buseshaving different radii of curvature, there can be employed a structurein which the first and second buses have a common tangent in theboundary between them, or a structure in which there is formed a thirdbus in such a manner that it extends astride the first and second buses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a section view of the main portions of a firstembodiment of a roller bearing according to the invention;

[0034]FIG. 2 is a section view of the main portions of a secondembodiment of a roller bearing according to the invention;

[0035]FIG. 3 is a section view of the main portions of a thirdembodiment of a roller bearing according to the invention;

[0036]FIG. 4 is a section view of the main portions of a fourthembodiment of a roller bearing according to the invention;

[0037]FIG. 5 is a section view of the main portions of a fifthembodiment of a roller bearing according to the invention;

[0038]FIG. 6 is a section view of the main portions of a sixthembodiment of a roller bearing according to the invention;

[0039]FIG. 7 is a section view of the main portions of a seventhembodiment of a roller bearing according to the invention;

[0040]FIG. 8 is a section view of the main portions of an eighthembodiment of a roller bearing according to the invention,

[0041]FIG. 9 is a section view of the main portions of a ninthembodiment of a roller bearing according to the invention;

[0042]FIG. 10 is a section view of the main portions of a tenthembodiment of a roller bearing according to the invention;

[0043]FIG. 11 is a section view of the main portions of a eleventhembodiment of a roller bearing according to the invention;

[0044]FIG. 12 is a graphical representation of surface pressuredistributions respectively obtained in an embodiment of a roller bearingaccording to the invention and in two kinds of conventional rollerbearings, or, comparison examples;

[0045]FIG. 13 is a graphical representation of surface pressuredistributions respectively obtained in the embodiment of a rollerbearing according to the invention and in the two comparison examplesshown in FIG. 12; and

[0046]FIG. 14 is a graphical representation of surface pressuredistributions respectively obtained in the embodiment of a rollerbearing according to the invention and in one of the two comparisonexamples shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Now, description will be given below in detail of the preferredembodiments of a roller bearing according to the invention withreference to the accompanying drawings. That is, FIGS. 1 to 10 arerespectively section views of the main portions of first to tenthembodiments of a roller bearing according to the invention.

[0048] As shown in FIG. 1(A), a roller bearing 10, which is a firstembodiment of the invention, comprises a plurality of substantiallyconical-shaped rollers 15 which are respectively interposed between aconcave-shaped race surface 12 formed on an outer race 11 and aconcave-shaped race surface 14 formed on an inner race 13.

[0049] As shown in FIG. 1(B), each roller 15 is structured such that thecentral portion of the rolling surface thereof is formed by a first bus17, whereas the portions of the rolling surface thereof, which arerespectively situated on the large-diameter side (in FIG. 1(B), on theright side) and on the small-diameter side (in FIG. 1(B), on the leftside which is not shown), are respectively formed by second buses 16.(In other words, as shown in FIG. 1(B), each roller 15 is structured insuch a manner that the central portion of the rolling surface is definedby rotating a first bus 17 about the axis of the roller 15, and theright and left side portions of the rolling surface are respectivelydefined by rotating second buses 16 about the axis of the roller 15.)Here, the radius of curvature of the first bus 17 is so set so as tosubstantially correspond to the buses of the concave-shaped racesurfaces 12 and 14, that is, it is set very slightly smaller than theradii of curvature of the buses of the concave-shaped race surfaces 12and 14, while the radius of curvature of the second bus 16 is setslightly smaller than the radius of curvature of the first bus 17.

[0050] And, since the first and second buses 17 and 16 are formed suchthat they have a common tangent line in the boundary area thereof, thereis eliminated a fear that the surface pressure can increase in theboundary portion 18 between first and second buses 17 and 16.

[0051] By the way, in order to prevent an increase in the surfacepressure in a specific portion in the roller bearing 10, as shown inFIG. 1(C), there may also be employed a roller 15A in which the portionthereof existing between the first and second buses 17 and 18 is formedby a third bus 19.

[0052] With use of this roller 15A, the surface pressure in the boundaryline 18A between the first and third buses 17 and 19, or the surfacepressure in the boundary portion 18B between the second and third buses16 and 19 can be reduced when compared with the surface pressure of theboundary portion 18 in the roller 15.

[0053] In the above-structured roller bearing 10, since the first bus 17in the roller 15 is formed in a convex shape and the radius of curvaturethereof is so set as to correspond to the buses of the concave-shapedrace surfaces 12 and 14, that is, it is set very slightly smaller thanthe radii of curvature of the buses of the concave-shaped race surfaces12 and 14, even when the axis shift angle between the outer race 11 andinner race 13 is small, or even when no axis shift occurs, theconvex-shaped rolling surfaces of the rollers 15 can be line contactedwith the concave-shaped race surfaces 12 and 14 over a sufficientlength. Accordingly, there is eliminated a fear that the surfacepressures between the race surfaces 12 and 14 and the respective rollers15 are increased.

[0054] And, in the roller bearing 10, because the radius of curvature ofthe second bus 16 is set smaller than the radius of curvature of thefirst bus 17 in each roller 15, the roller bearing 10 is capable ofcoping with a large axis shift angle produced between the outer andinner races.

[0055] Therefore, when compared with the conventional roller bearing,the present roller bearing 10 is capable of coping with a large axisshift angle produced between the outer and inner races, and also, evenwhen the axis shift angle between the outer race 11 and inner race 13 issmall, can control an increase in the surface pressures between theconcave-shaped race surfaces 12, 14 and the respective rolling members15.

[0056] In addition to this, in this embodiment, a center of curvature ofthe first bus 17 is positioned at a position further than the axis ofthe roller bearing, so that the edge load can be remarkably andeffectively suppressed.

[0057] As shown in FIG. 2, a roller bearing 20, which is a secondembodiment of the invention, comprises a plurality of substantiallyconical-shaped rollers 25 which are respectively interposed between aconvex-shaped race surface 22 formed on an outer race 21 and aconvex-shaped race surface 24 formed on an inner race 23.

[0058] Each of the rollers 25 is structured such that the centralportion of the rolling surface thereof is formed by a firstconcave-shaped bus 27, whereas the two end portions of the rollingsurface thereof are formed by second concave-shaped buses 26 and 26respectively.

[0059] Here, the radius of curvature of the first bus 27 is so set as tocorrespond to the buses of the convex-shaped race surfaces 22 and 24,that is, it is set very slightly larger than the radii of curvature ofthe buses of the convex-shaped race surfaces 22 and 24, while the radiiof curvature of the second buses 26 are set slightly larger than theradius of curvature of the first bus 27. And, the roller 25 is alsostructured such that the first bus 27 and second buses 26, 26 have acommon tangent line in the boundary portion 28 between them.

[0060] With use of the roller bearing 20 as well, there can be obtaineda similar effect to the previously described roller bearing 10.

[0061] As shown in FIG. 3, a roller bearing 30, which is a thirdembodiment of the invention, comprises a plurality of substantiallyconical-shaped rollers 35 which are respectively interposed between theconcave-shaped race surface 32 of an outer race 31 and theconcave-shaped race surface 34 of an inner race 33.

[0062] Each of the rollers 35 is structured such that the centralportion of the rolling surface thereof is formed by a firstconvex-shaped bus 37, while the two end portions of the rolling surfacethereof are respectively formed by second convex-shaped buses 36 and 36.The radius of curvature of the first bus 37 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 32 and 34, that is, it is set very slightly smaller than theradii of curvature of the buses of the concave-shaped race surfaces 32and 34, whereas the radii of curvature of the second buses 36 and 36 areset slightly smaller than the radius of curvature of the first bus 37.And, the roller 35 is also structured such that the first bus 37 andsecond buses 36, 36 have a common tangent line in the boundary portion38 between them.

[0063] The present roller bearing 30, when compared with theconventional roller bearing, not only can cope with a large axis shiftangle to be produced between the outer and inner races 31 and 33, butalso, even when the axis shift angle between the outer and inner races31 and 33 is small, can control an increase in the surface pressurebetween the concave-shaped race surfaces 32, 34 and the respectiverolling members 35.

[0064] As shown in FIG. 4, a roller bearing 40, which is a fourthembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 45 which are respectively interposed between aconcave-shaped race surface 42, which is formed between a pair of ribs41A and 41A respectively disposed in an outer race 41, and aconcave-shaped race surface 44 formed on an inner race 43. Each of therollers 45 is structured such that the central portion of the rollingsurface thereof is formed by a first convex-shaped bus 47, while the twoend portions of the rolling surface thereof are respectively formed bysecond convex-shaped buses 46 and 46.

[0065] Referring in more particular to the structure of the roller 45,the radius of curvature of the first bus 47 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 42 and 44, that is, it is set very slightly smaller than theradii of curvature of the buses of the concave-shaped race surfaces 42and 44, and the radii of curvature of the second buses 46 and 46 are setslightly smaller than the radius of curvature of the first bus 47; and,the first bus 47 and the second buses 46, 46 have a common tangent intheir respective boundary portions 48.

[0066] With use of the present roller bearing 40 as well, there can beobtained a desired effect.

[0067] As shown in FIG. 5, a roller bearing 50, which is a fifthembodiment of the invention, comprises a plurality of barrel-shapedrollers 55 which are respectively interposed between a concave-shapedrace surface 52 of an outer race 51 and a concave-shaped race surface54, which is interposed between a pair of ribs 53A and 53A respectivelydisposed on an inner race 53. Each of the rollers 55 is structured suchthat the central portion of the rolling surface thereof is formed by afirst convex-shaped bus 57, while the two end portions of the rollingsurface thereof are respectively formed by second convex-shaped buses 56and 56.

[0068] Referring in more particular to the structure of the roller 55,the radius of curvature of the first bus 57 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 52 and 54, that is, the former is set very slightly smallerthan the latter, and the radii of curvature of the second buses 56 and56 are respectively set slightly smaller than the radius of curvature ofthe first bus 57; and, the first bus 57 and the second buses 56, 56 havea common tangent in their respective boundary portions 58.

[0069] According to the present roller bearing 50 as well, there can beobtained a desired effect.

[0070] As shown in FIG. 6, a roller bearing 60, which is a sixthembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 65 which are respectively interposed between aconcave-shaped race surface 62, which is formed between a pair of ribs61A and 61A respectively disposed in an outer race 61, and aconcave-shaped race surface 64 which adjoins a rib 63A disposed on oneend side of an inner race 63. Each of the rollers 65 is structured suchthat the central portion of the rolling surface thereof is formed by afirst convex-shaped bus 67, while the two end portions of the rollingsurface thereof are respectively formed by second convex-shaped buses 66and 66

[0071] Referring in more particular to the structure of the roller 65,the radius of curvature of the first bus 67 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 62 and 64, that is, the former is set very slightly smallerthan the latter, and the radii of curvature of the second buses 66 and66 are respectively set slightly smaller than the radius of curvature ofthe first bus 67; and, the first bus 67 and the second buses 66, 66 havea common tangent in their respective boundary portions 68.

[0072] Of course, according to the present roller bearing 60 as well,there can be obtained a desired effect.

[0073] As shown in FIG. 7, a roller bearing 70, which is a seventhembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 75 which are respectively interposed between aconcave-shaped race surface 72, which is formed between a pair of ribs71A and 71A respectively disposed in an outer race 71, and aconcave-shaped race surface 74 which adjoins a rib 73A disposed on oneend side of an inner race 73. Each of the rollers 75 is structured suchthat the central portion of the rolling surface thereof is formed by afirst convex-shaped bus 77,. while the two end portions of the rollingsurface thereof are respectively formed by second convex-shaped buses 76and 76.

[0074] Referring in more particular to the structure of the roller 75,the radius of curvature of the first bus 77 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 72 and 74, that is, the former is set very slightly smallerthan the latter, and the radii of curvature of the second buses 76 and76 are respectively set slightly smaller than the radius of curvature ofthe first bus 77; and, the first bus 77 and the second buses 76, 76 havea common tangent in their respective boundary portions. Of course,according to the present roller bearing 70 as well, there can beobtained a desired effect.

[0075] As shown in FIG. 8, a roller bearing 80, which is an eighthembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 85 which are respectively interposed between aconcave-shaped race surface 82 formed on an outer race 81 and aconcave-shaped race surface 84 formed on an outer race 83. Each of therollers 85 is structured such that the central portion of the rollingsurface thereof is formed by a first convex-shaped bus 87 and the twoend portions of the rolling surface thereof are respectively formed bysecond convex-shaped buses 86 and 86.

[0076] Referring in more particular to the structure of the roller 85,the radius of curvature of the first bus 87 is so set as to correspondto the radii of curvature of the buses of the concave-shaped racesurfaces 82 and 84, that is, the former is set very slightly smallerthan the latter, and the radii of curvature of the second buses 86 and86 are respectively set slightly smaller than the radius of curvature ofthe first bus 87. And, the roller 85 is also structured such that thefirst bus 87 and second buses 86, 86 have a common tangent line in theboundary portion 88 between them.

[0077] Of course, according to the present roller bearing 80 as well,there can be obtained a desired effect.

[0078] As shown in FIG. 9, a roller bearing 90, which is a ninthembodiment of the invention, comprises a plurality of substantiallycylindrical-shaped rollers 95 which are respectively interposed betweena convex-shaped race surface 92 of an outer race 91, and a convex-shapedrace surface 94 of an inner race 93.

[0079] Each of the rollers 95 is structured such that the centralportion of the rolling surface thereof is formed by a firstconcave-shaped bus 97, while the two end portions of the rolling surfacethereof are respectively formed by second concave-shaped buses 96 and96. more particularly, in the present roller 95, the radius of curvatureof the first bus 97 is so set as to correspond to the radii of curvatureof the buses of the convex-shaped race surfaces 92 and 94, that is, theformer is set very slightly smaller than the latter. Also, the radii ofcurvature of the second buses 96 and 96 are respectively set slightlysmaller than the radius of curvature of the first bus 97; and, the firstbus 97 and the second buses 96, 96 have a common tangent in theirrespective boundary portions 98.

[0080] In addition to this, in this embodiment, a center of curvature ofthe convex-shaped race surface 94 of an inner race 93 is positioned at aposition further than the axis of the roller bearing, so that the edgeload can be remarkably and effectively suppressed.

[0081] Of course, according to the present roller bearing 90 as well,there can be obtained a similar effect to the above-mentioned rollerbearing 80.

[0082] Although aforementioned explanations are given to the rollingsurface of the roller which is formed by a plurality of buses containingthe first and second buses, an explanation regarding another embodimentsin which at least one of the race surfaces of the outer and inner racescomprises a plurality of buses containing the first and second buseswill be hereinafter described.

[0083] As shown in FIG. 10, a roller bearing 100, which is a tenthembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 105 which are respectively interposed between aconvex and concave mixture shaped race surface 102 of an outer race 101,and a concave shaped race surface 104, which is formed between a pair ofribs 103A and 103A of an inner race 103.

[0084] The convex and concave mixture shaped race surface 102 isstructured such that the central portion of the rolling surface thereofis formed by a first concave-shaped bus 107A, while the two end portionsare respectively formed by second concave-shaped buses 106A and 106A.

[0085] More particularly, the radius of curvature of the first bus 107Ais so set as to substantially correspond to the radii of curvature ofthe buses of the rolling surface of the roller 105, that is, the formeris set very slightly larger than the latter. Also, the radii ofcurvature of the second buses 106A and 106A are respectively setslightly larger than the radius of curvature of the first bus 107A; and,the first bus 107A and the second buses 106A and 106A have a commontangent in their respective boundary portions 108A.

[0086] However, note that the radii of curvature of the second buses106A and 106A can be modified not only to be much larger than the radiusof curvature of the first bus 107A but also to be slightly smaller thanthe radius of curvature of the first bus 107A, if a convex shape of itsrace surface is kept maintained.

[0087] The concave-shaped race surface 104 is structured such that thecentral portion of the rolling surface thereof is formed by a firstconcave-shaped bus 107B, while the two end portions are respectivelyformed by second concave-shaped buses 106B and 106B. The radius ofcurvature of the first bus 107B is so set as to substantially correspondto the radii of curvature of the buses of the rolling surface of theroller 105, that is, the former is set very slightly larger than thelatter. Also, the radii of curvature of the second buses 106B and 106Bare respectively set slightly larger than the radius of curvature of thefirst bus 107A; and, the first bus 107B and the second buses 106B, 106Bhave a common tangent in their respective boundary portions 108B.

[0088] On the other hand, the concave-shape race surface 104 of theinner race 103 in the embodiment can be modified to be a convex andconcave mixture shape as well as the race surface 102 of the outer race101.

[0089] Of course, according to the present roller bearing 100 as well,there can be obtained a similar effect to the above-mentioned rollerbearing.

[0090] As shown in FIG. 11, a roller bearing 110, which is a eleventhembodiment of the invention, comprises a plurality of substantiallybarrel-shaped rollers 115 which are respectively interposed between aconcave-shaped race surface 112 of an outer race 111, and aconcave-shaped race surface 114, which is formed between a pair of ribs113A and 113A of an inner race 113.

[0091] The concave-shaped race surface 112 is structured such that thecentral portion of the rolling surface thereof is formed by a firstconcave-shaped bus 117A, while the two end portions are respectivelyformed by second concave-shaped buses 116A and 116A. In addition, theconcave-shaped race surface 114 is structured such that the centralportion of the roiling surface thereof is formed by a firstconcave-shaped bus 117B, while the two end portions are respectivelyformed by second concave-shaped buses 116B and 116DB.

[0092] More particularly, the radius of curvature of the first buses117A and 117B are so set as to substantially correspond to the radii ofcurvature of the buses of the rolling surface of the roller 115, thatis, the formers are set very slightly larger than the latter. Also, theradii of curvature of the second buses 116A, 106A, 116B and 116B arerespectively set slightly larger than the radius of curvature of thefirst buses 117A and 117B; and, the first buses 107A and 107B and thesecond buses 106A, 106A, 106B and 106B have a common tangent in theirrespective boundary portions 10A and 108B.

[0093] On the other hand, the concave-shape race surface 114 of theinner race 113 in the embodiment can be modified to be a convex andconcave mixture shape as well as the race surface 102 of the outer race101 in the tenth embodiment.

[0094] Of course, according to the present roller bearing 110 as well,there can be obtained a similar effect to the above-mentioned rollerbearing.

[0095] Note that, in the first to ninth embodiment, it is possible tomodify it so as to form its race surface of the inner and/or outer racewith a plurality of buses, instead of the rolling surface of the rollingmember.

[0096] Of course, according to the present roller bearing 110 as well,there can be obtained a similar effect to the above-mentioned rollerbearing.

[0097] Next, as the present inventors have analyzed and studied atypical example of the roller bearings constructed in accordance withthe invention as to the presence or absence of an edge load to beproduced between the outer and inner races thereof at every axis shiftangle, description will be given below of the analysis results thereoftogether with the analysis results of the conventional roller bearings,that is, comparison examples with reference to Table 1. TABLE 1 Axisshift (Unit: Minute) 0 3 6 9 12 Embodiment 1 ∘ ∘ ∘ ∘ ∘ ComparisonExample 1 ∘ x x x x Comparison Example 2 ∘ ∘ ∘ ∘ ∘

[0098] That is, in our test, in all of the embodiment 1 and comparisonexamples 1 and 2, the outside diameter of an outer race was set for 310mm, the inside diameter of an inner race was set for 200 mm, thethicknesses of the outer and inner races were both set for 66 mm, andthere was employed a roller having an axial length of 49 mm. And, underthe conditions that a radial load is 85 kN and an axial load is 42 kN,the inventors analyzed whether any edge load could occur or not at everyaxis shift angle, and evaluated the results using marks ∘ and X.

[0099] Here, the embodiment 1 is basically structured in accordance withthe above-mentioned first embodiment of the invention; in particular,the radii of curvature of the respective concave-shaped race surfacesthereof were set for 500 mm, the radius of curvature of the first bus ofeach roller was set for 490 mm, and the radius of curvature of thesecond bus of each roller was set for 425 mm.

[0100] On the other hand, in the comparison example 1, the radii ofcurvature of the buses of the respective race surfaces thereof were setfor 500 mm, the rolling surface of each roller was formed by a singlebus, and the radius of curvature thereof was set for 490 mm

[0101] Also, in the comparison example 2, the radii of curvature of thebuses of the respective race surfaces thereof were set for 500 mm, therolling surface of each roller was formed by a single bus, and theradius of curvature thereof was set for 450 mm.

[0102] According to Table 1, in the embodiment 1, it is found that,although the radius of curvature of the second bus of the roller is setsmaller than the radius of curvature of the first bus thereof and thusthe axes of the outer and inner races can be shifted from each other andthe roller can be thereby inclined, because the end portions of therolling surface of the roller are not contacted with the race surfacesof the outer and inner races, the maximum allowed angle of the axisshift is large. In the comparison example 2 as well, because the radiusof curvature of the rolling surface of the roller is small, similarly tothe embodiment 1, the maximum allowed angle of the axis shift is large.

[0103] Here, FIGS. 12 to 14 show the axial-direction surface pressuredistribution of the roller with respect to the concave-shaped racesurface on the inner race side in the embodiment 1 as well as in thecomparison examples 1 and 2. In particular, FIG. 12 shows the surfacepressure distribution when the axes of the inner and outer races are notshifted at all; FIG. 13 shows the surface pressure distribution when theaxis shift between the axes of the inner and outer races is 6 minutes;and FIG. 14 shows the surface pressure distribution when the axis shiftbetween the axes of the inner and outer races is 12 minutes.

[0104] In the comparison example 1, when the axes of the inner and outerraces are not shifted at all, the surface pressure is the lowest; but,when the axes of the inner and outer races are shifted from each other,there occurs an edge stress. And, in the comparison example 2, becausethe radius of curvature of the rolling surface of the roller is small,even if the axis shift between the axes of the inner and outer races islarge, no edge stress occurs; but, when the axes of the inner and outerraces are not shifted at all, or when the axis shift between the axes ofthe inner and outer races is small, in the central portion of theroller, the surface pressure rises in a quadratic curve manner and thusthe surface pressure in the central portion of the roller is larger thanthe other two examples. Also, from these figures, it can be found that,in the embodiment 1, when the axes of the inner and outer races are notshifted at all, the surface pressure thereof is almost the same as thecomparison example 1 and is lower than in the comparison example 2; and,even when the axes are shifted from each other, no edge stress occurs.

[0105] From the above-mentioned results, when use in various inclinationconditions is taken into account, the embodiment 1 is found best.

[0106] By the way, a roller bearing according to the invention is notlimited to the respective embodiments described hereinbefore but thematerial, shapes, dimensions, radii of curvature, number, settingpositions and the like of the concave-shaped race surfaces, outer race,inner race, rolling members, convex-shaped buses, convex-shaped racesurfaces, concave-shaped buses and the like can be selected arbitrarily,provided that they are able to achieve the present invention.

[0107] The present invention is based on Japanese Patent Application No.Hei. 10-183429, which is incorporated herein by reference.

[0108] While there has been described in connection with the preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed, therefore, to cover inthe appended claim all such changes and modifications as fall within thetrue spirit and scope of the invention.

[0109] As has been described heretofore, according to the invention, thepresent roller bearing is structured such that not only the racesurfaces of the inner and outer races and the rolling surfaces of therollers are contacted with each other in the form of mutual contactbetween the convex-shaped buses and their corresponding concave-shapedbuses, but also there are produced relatively large clearances betweenthe race surfaces of the inner and outer races and the respectivetwo-end portions of the rolling surfaces of the rollers. Thanks to this,even when the axis shift angle between the outer and inner races issmall, or even when no shift is present between the axes of the outerand inner races is small, the present roller bearing can relieve thesurface pressures between the respective race surfaces and therespective rolling members, can control occurrence of an edge load, andcan cope with a large axis shift between the inner and outer races whencompared with the conventional roller bearing.

What is claimed is:
 1. A roller bearing comprising: an outer raceincluding an outer race surface which is formed on the inner peripheralsurface thereof and is defined by rotating an outer race surfacedefining bus about an axis thereof; an inner race including an innerrace surface which is formed on the outer peripheral surface thereof andis defined by rotating an inner race surface defining bus about theaxis; and a plurality of rolling members respectively interposed betweensaid outer and inner race surfaces, an outer peripheral surface of eachof said rolling members being defined by rotating a rolling surfacedefining bus about its axis, wherein at least one of said outer racesurface defining bus, said inner race surface defining bus and therolling surface defining bus comprises a first radius of curvature, andeach of the others of said outer race surface defining bus, said innerrace surface defining bus and the rolling surface defining bus comprisesa first bus having a second radius of curvature which is different fromthe first radius of curvature and substantially disposed at a center inan axial direction of the roller bearing and second buses disposed bothsides of the first bus, each of the second buses having a third radiusof curvature which is different from the first radius of curvature andis also different from said second radius of curvature.
 2. The rollerbearing according to claim 1 , wherein each of said outer race surfacedefining bus and said inner race surface defining bus has the firstradius of curvature, and said rolling surface defining bus comprises thefirst bus and the second buses.
 3. The roller bearing according to claim2 , wherein each of said outer race surface and said inner race surfaceis a concave shape, and wherein said first radius is larger than saidsecond radius, and said second radius is larger than said third radius.4. The roller bearing according to claim 2 , wherein each of said outerrace surface and said inner race surface is a convex shape, and whereinsaid first radius is smaller than said second radius, and said secondradius is smaller than said third radius.
 5. The roller bearingaccording to claim 2 , wherein said first bus and at least one of saidsecond buses are directly and continuously connected each other and havea common tangent line in a boundary position therebetween.
 6. The rollerbearing according to claim 3 , wherein said first bus and at least oneof said second buses are directly and continuously connected each otherand have a common tangent line in a boundary position therebetween. 7.The roller bearing according to claim 4 , wherein said first bus and atleast one of said second buses are directly and continuously connectedeach other and have a common tangent line in a boundary positiontherebetween.
 8. The roller bearing according to claim 2 , wherein eachof said rolling members is formed into a substantially cylindricalshape.
 9. The roller bearing according to claim 2 , wherein each of saidrolling members is formed into a substantially conical shape.
 10. Theroller bearing according to claim 2 , wherein each of said rollingmembers is formed into a substantially barrel shape.
 11. The rollerbearing according to claim 1 , wherein said first bus and at least oneof said second buses are directly and continuously connected each otherand have a common tangent line in a boundary position therebetween. 12.The roller bearing according to claim i, wherein each of said outer racesurface defining bus and said inner race surface defining bus comprisesthe first bus and the second buses, and said rolling surface definingbus has the first radius of curvature.
 13. The roller bearing accordingto claim 12 , wherein each of said outer race surface and said innerrace surface is a concave shape, and wherein said first radius issmaller than said second radius, and said second radius is smaller thansaid third radius.
 14. The roller bearing according to claim 12 ,wherein said first bus and at least one of said second buses aredirectly and continuously connected each other and have a common tangentline in a boundary position therebetween.
 15. The roller bearingaccording to claim 13 , wherein said first bus and at least one of saidsecond buses are directly and continuously connected each other and havea common tangent line in a boundary position therebetween.
 16. A rollerbearing comprising: an outer race including a concave-shaped racesurface formed on the inner peripheral surface thereof; an inner raceincluding a concave-shaped race surface formed on the outer peripheralsurface thereof; and a plurality of substantially cylindrical-shapedrolling members respectively interposed between said concave-shaped racesurfaces of said outer and inner races, the outer peripheral surface ofeach of said rolling members being formed by a convex-shaped bus,wherein each of central portions in one of said concave-shaped racesurfaces of said outer and inner races and said outer peripheralsurfaces of said rolling members is formed by a first bus having a givenradius of curvature, and two end portions respectively adjoining saidcentral portion are respectively formed by second buses each having aradius of curvature which causes said two end portions to be separatefrom the other of said concave-shaped race surfaces of said outer andinner races and said outer peripheral surfaces of said rolling members.17. A roller bearing comprising: an outer race including a convex-shapedrace surface formed on the inner peripheral surface thereof; an innerrace including a convex-shaped race surface formed on the outerperipheral surface thereof; and a plurality of substantiallycylindrical-shaped rolling members respectively interposed between saidconvex-shaped race surfaces of said outer and inner races, the outerperipheral surface of each of said rolling members being formed by aconcave-shaped bus, wherein each of central portions in one of saidconvex-shaped race surfaces of said outer and inner races and said outerperipheral surfaces of said rolling members is formed by a first bushaving a given radius of curvature and two end portions respectivelyadjoining said central portion are respectively formed by second buseseach having a radius of curvature which causes said two end portions tobe separate from the other of said convex-shaped race surfaces of saidouter and inner races and said outer peripheral surfaces of said rollingmembers.